Plug valves, including ball valves, which are rotated through ninety degrees between their full open and closed positions, have long been used for flow control purposes. If the plug is intermediate its extreme positions, i.e. partially open, it provides two orifices in series, which are connected by a fixed volume. This throttles gas flow through the valve and is particularly effective where a low pressure differential exists across the valve element. There are, however, many services wherein the valve is required to absorb large amounts of energy and to effect substantial pressure drops. This could occur, for example, in the case of pipeline gas flow to a storage tank or to atmosphere or in a variety of flow control requirements involving high rangeability.
Conventional ball and plug valves create very high fluid velocities when throttling under high differential conditions, and these high velocities may result in turbulence, cavitation and noise at excessive and damaging levels.